Nitrogen-Containing Organic Electrode Materials for Li-Ion Batteries and Beyond

Abstract

The commercial Li-ion batteries cause severe environmental challenges such as heavy metal pollution and global warming due to the use of toxic cobalt-based inorganic materials and the huge amount of CO2 release from the battery material production and recycling process. To overcome these environmental challenges, the inexpensive, abundant, environmentally benign and sustainable organic electrode materials and polymers provide an ideal solution. In our work, we demonstrated that the nitrogen-containing organic materials such as carboxylated azo compounds and imine-based polymers are promising electrode materials for Li-ion batteries and beyond. As an example, poly-hexaazatrinaphthalene (PHATN), which is an electron-deficient, rigid and planar aromatic discotic system with pyrazine functional groups, enables fast charge/discharge of Na, Mg and Al ions with high cycling stability. In Na-ion batteries (NIBs), PHATN delivers a reversible capacity of 165 mA h/g and 100 mA h/g after ultra-long 10,000 and 50,000 cycles at ultra-high current densities of 2 A/g (5C) and 10 A/g (25C), respectively. These capacity delivery and retention, to our best knowledge, are the highest among both organic and inorganic cathodes reported for NIBs. The exceptional rate and cycle life seen in NIBs carry over to RMBs and RABs as well. The mechanism for exceptional rate and cycling performance of PHATN is investigated using density functional theory (DFT), ex situ Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). For the first time, we proved that imine group (C=N) in the conjugated polymer can reversibly react with Mg2+ and Al3+ in the rechargeable batteries. This work demonstrates that the pyrazine-based polymer cathode is promising for developing environmentally benign, high-energy-density, fast and ultra-stable rechargeable batteries.